Girard Desargues (February 21 or March 2, 1591-October 1661) was a French mathematician and engineer, who is considered one of the founders of projective geometry. He is the eponym of Desargues' theorem and of the crater Desargues on the Moon.
Born in Lyon, Desargues came from a family devoted to service to the French crown. His father was a royal notary, an investigating commissioner of the Seneschal's court in Lyon (1574), the collector of the tithes on ecclesiastical revenues for the city of Lyon (1583) and for the diocese of Lyon.
As an architect, Desargues planned several private and public buildings in Paris and Lyon. As an engineer, he designed a system for raising water that he installed near Paris. It was based on the use of the at the time unrecognized principle of the epicycloidal wheel.
His work was rediscovered and republished in 1864. His works were subsequently collected in L'oeuvre mathématique de Desargues (ed. by René Taton; Paris, 1951).
Late in his life, Desargues published a paper with the cryptic title of DALG. The most common theory about what this stands for is Des Argues, Lyonnais, Géometre, proposed by Henri Brocard.